Good carbs like celery and carrots will never make you fat. Bad carbs like cake will, but you don't need to know the whole science of glycemic load. You need to re-learn how to eat so you can become thin and healthy. Find out about fastest way to lose weight, most effective exercise, good and bad fats, water retention and secret trick used by models to flatten their tummy before an event.
Reading a book will take you hours but the information on a post, taking minutes to read, is not enough. The webpage below has just enough to know what you need to know. Links page has gov. BMI calculater to find out just how much overweight you are (teens plug in your age to compare to others your age). Learn the science of how to nourish your body thin, instead of starving your body fat.
http://www.phifoundation.org